1. Technical Field
The present invention relates to a method, and associated structure, for adhesively coupling a chip to an organic chip carrier.
2. Related Art
A well-known method of adhesively coupling a chip to a chip carrier is that of controlled collapse chip connection ("C4"). With the C4 method, a C4 solder structure ("C4 structure") attached to the chip is coupled to a pad on the chip carrier by an interfacing solder bump that rests on the pad. Heating liquefies the solder bump to generate reflowed solder. Subsequent cooling of the reflowed solder effectuates an adhesive coupling between the C4 structure and the pad, which in turn mechanically and conductively couples the chip to the chip carrier.
If the chip carrier comprises a highly pliable material, such as a pliable organic material, the aforementioned C4 method is prone to failure inasmuch as the C4 structure may not properly contact the pad of the chip carrier. Such contact reliability problems result from an inability of the chip carrier to maintain flat surfaces during reflow, coupled with a difficulty of the reflowed solder to maintain contact with both the C4 structure and the pad of the chip carrier. FIGS. 7 and 8 each illustrate such contact reliability problems arising from an inability of the chip carrier to maintain flat surfaces during reflow. In FIG. 7, a chip carrier 200 is intended to be conductively coupled to a surface 250 of a substrate 240 of a chip carrier, by use of C4 structures 210, 220, and 230. Because the surface 250 has a concavity in a direction 260 away from the chip 200, C4 structures 210 and 230 are unable to maintain contact with the surface 250. In FIG. 8, a chip carrier 300 is intended to be conductively coupled to a surface 350 of a substrate 340 of a chip carrier, by use of C4 structures 310, 320, and 330. Because the surface 350 has a concavity in a direction 360 toward the chip 300, C4 structure 320 is unable to maintain contact with the surface 350.
A method is needed during reflow of the solder bump to constrain the chip carrier to have a flat structure, and to constrain the reflowed solder to maintain contact with both the C4 structure and the pad of the chip carrier.